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MG MGB Technical - Throttle/Choke Return Springs


For an early B (1964) does anyone have a picture of the return springs set up.I have 3 springs at one end attached to the heat shield, one to each carb and one to the throttle, should there be a 4th attached to choke? If so where does each end attach.

thanks

Les
Les Jacobs

les
no there isnt a fourth spring
if you need a pici can email one to you from my 63 rebuild
ste
Ste Brown

Ste

Thank you for the info, I wasn't sure as my 68 C has 4 springs including the choke, a pic would be nice. You can send it to les@ljacobsconsulting.net

Les
Les Jacobs

As Ste says there isn't an external return spring for the choke cable, however there should be a spring behind the cam on the carb itself.
Paul Hunt 2

Out of curiosity, There are three bent out taps for the carburettor springs but there are also holes at the base of the plate just to the side of the bent tabs.

What pulls the choke back down?
BEC Cunha

My 69 has 4 springs. Three on throttle and one on choke. My Moss catelogue shows 4 return springs for the cars 62 to 73 - throttle and choke.

The Choke spring on mine mounts in the hole through the lower edge of the heat shield. The throttle springs mount to holes in the 'bent out tabs'.

Regards
Roger
Roger T

Roger

Thanks for your comment. I had a look at the Moss Cat., Engine controls page, item number 41 , choke return, 2 required, I think refers to the springs attached from the heat shield to the ends of the throttle linkage even though it looks like it is attached to the choke ( why 2?) Item #27, accelerator return is the spring attached to the throttle cable lever. Total is 3 springs. I also inquired with the "experts" at my local club and an mg specialist mechanic in my area and all say 3 springs. However I am still not 100% convinced until I have a close look at the original parts Manuel for the 1964 year. Its unlikely but in 1969 an additional spring may have been added by BMC or was added by the previous owner.

Anybody care to comment further ?


Les
Les Jacobs

My 73 roadster has one return spring on the end of the throttle cable plus one on each half of the *throttle* spindle, all going to hooks or holes in the heat shield. The Leyland Parts Catalogue specifies all 3 from the beginning of production. There may be one on the choke as well making 4, but don't remember it on my car (haven't got it to hand). Because of the 'pull and release' action of the accelerator, and what effect it has on vehicle motion, it is far more important that the accelerator doesn't stick than the 'pull-push' that is possible with the choke, hence the multiple springs on the accelerator. It's possible that originally there *were* only the two on the interconnecting shafts and not one on the accelerator cable, but if there had been problems of non-return the 3rd may have been fitted retrospectively which is why it is shown as 3 in the Parts Catalogue. As such it would be advisable to fit it!
Paul Hunt 2

les
ive just picked up a 65 engine and box and there is 4 springs on that engine
the accelerator spring is in the little hole on the shield lip and the centre tab is for the choke
i am not sure if mine has 4 as the pic i sent you was during my rebuild stage
ste
Ste Brown

Thanks Ste, the mystery continues

Well several variations but which one is correct; 3 or 4 springs, and if
4 springs are correct where does the 4th spring attach for the choke, the little hole on the heat shield or on the heat shield tab.

Anybody?

Les
Les Jacobs

Les,

I'm not sure that there is a great deal of difference whether the carb/throttle springs mount in the tabs or the holes on the bottom edge of the shield. Of importance, I think, might be that all three of those mount to the same horizontal plane - giving even stretch on the springs. Of course this assumes some degree of uniformity in spring quality.

Prior to my carb rebuild and new springs being fitted those three on mine were in the bottom holes. I presume this was an attempt to take up some degree of stretch in the older springs. The rebuilders fitted the new to the tab position. That leaves my choke spring fitted to the centre bottom edge.

Checked my Moss catelogue again. Moss Europe 2001. Page 23, "Engine Controls for HS type Carbs 18G-18V ('62-'73)" - "Item #40 - part #AEC2075 - Qty=4 - Return Spring - Remarks - Throttle and Choke."

My Leyland workshop manual does not help. It shows expleded views of the Carb components and linkages but nothing to do with the heat shield/carb mounting.

Maybe its an Aussie thing. We like to do things thoroughly!

Regards
Roger
Roger T

les
if this engine is correct
accelerator to hole in heat shield
choke to centre tab
all the springs seem to fit in line nicely like that so id say that way
if your choke cable wont lock properly wont the choke spring keep pulling it in
maybe its missing to stop choke cable problems??????
Ste Brown


Thank you all for your comments, however still not being satisfied I contacted Burlen Fuel Systems, the current suppliers of SU carbs . This is their response:


Dear Sir,

Thank you for your enquiry,
There are only three springs fitted, not on the choke cable fitment.

Kind Regards
Burlen Fuel Systems Ltd



Jack Boswell
Customer Services


Les Jacobs

Another Abington oddity.

If there is not a spring on the choke, how does it fully return? Given there is a good 4 inches of cable when the choke is closed, if something did not pull it down, wouldn't there be the potential that it woudl not fully close?
BEC Cunha

The choke *is* a push/pull control, unlike the accelerator which is pull and release, but then again it *is* a stranded cable and not solid so not much strength in the 'push' direction. FWIW I subsequently came across an old picture of my linkages which despite the low resolution definitely shows a spring - http://www.mgb-stuff.org.uk/images/linkage1.jpg. The choke spindle runs across the middle of the photo and its return spring goes down from there, to the heat shield, just to the right of the finger on the accelerator spindle.

The Parts Catalogue lists a 'spring-cable return' amongst the choke components, qty 1, from car number 101 to 332032 and 'spring-choke return', qty 1 from car number 332033 to 76, both for all markets.

It also lists 2 springs in the list of parts for the accelerator also from car 101 to 76 for the UK, and for twin carb cars elsewhere. Curiously it also lists 2 springs for the Zenith, albeit a different part number.

Only 1 spring is specified for automatics, possibly the extension of the cable having a further return spring at the auto box.

For 77 on there is only one entry for springs, throttle return, qty 2, North America only!
Paul Hunt 2

Yes Paul, that is pretty much where my choke spring runs.

Regards
Roger
Roger T

Roger, Paul

Do your choke knobs turn to get a lock position?

The knob on my car does not have a lock feature. My 68 MGC does have a lock position( different type knob,) and does have a return spring; in fact it is attached to the heat shield tab.

Regards

Les

Les Jacobs

Les,

Yes, a lock position. The knob is drawn out and rotated anti-clockwise to hold it, despite the fact that the Drivers Handbook advises to turn it clockwise!

Must be the equator again!!

Regards
Roger
Roger T

See page 53, in the book "MGB, The Illustrated History", by Wood & Burrell. Lovely B&W factory sideview photos of the MGB engine, showing 4-springs in place. Admittedly, these are presumably pre-production vintage, but interesting none the less.
Terrence Goodell

Terrence

Good find! I have a copy of the book and you are quite right, 4 springs and both the throttle and choke seem to be attached to the heat shield tab.

Thanks

Les
Les Jacobs

Les - if it turns but doesn't lock (definitely clockwise to lock with mine, and indicated as such by arrows on the round knobs) wear can be the cause. The shaft on the inner has a profile something like a cam, but the 'lobe' of the cam covers about 180 degrees and the 'heel' the rest. Sitting across this cam under a spring-clip is something like a woodruff key. In the normal push/pull orientation of the choke the woodruff key sits over the cut-away part of the 'cam' i.e. the heel'. When you want to lock the choke you turn it clockwise (just over 45 degrees) and as you do so the leading edge of the 'lobe' lifts the key against the spring until it is fully on top of the lobe and the spring pressure holds it in that position.

Over time both the key and the cam wear, and if you can lock the knob in some positions which you don't normally use (like fully or almost fully home) then this will be the problem. This wear is usually visible on the shaft as a 'ramp' at the point of transition from heel to lobe, whereas on the unworn portion (about the first inch in from the knob) you can see an 'instant' transition from heel to lobe with no ramp.

However its possible the inner may be twisted in the 'release' direction of rotation which is overcoming the power of the lock, you can try disconnecting the inner from the carbs and twisting it in the other direction as you pull it back and fore a bit so that it tends to twist the knob *into* the locking position rather than away from it. I have also heard of a way of reversing something to use new areas of presumably the cam or the key, but having looked at an old one of mine you may be able to get away with this if it is the key that is worn, by turning it round the other way, but if it is the shaft that is worn there is nothing you can (reasonably) do about it short of replacement.

Paul Hunt 2

Paul

Thank you, however I should have mentioned that this is a new knob (NOS), installed by my local MG mechanic.

Regards

Les
Les Jacobs

What is engraved on the knob (and it should be a knob and not a T-handle)? Should be simply 'C' for all Mk1s. Does the knob twist at all? Should twist a fraction over *90* degrees (not 45 as I wrote earlier) if there is provision for a locking action. The shaft cross-section is basically a semi-circle of one radius and another semi-circle of a bigger radius, with the hole in the casting on the end of the outer being similar but the larger radius hole is about 270 degrees and the smaller only 90 degrees, which is what allows the knob to be twisted 90 degrees (see http://www.mgb-stuff.org.uk/wn_fuelframe.htm and click on 'Choke Control').

If it is new perhaps you just aren't twisting it hard enough, or maybe it needs a bit of grease on the wedge under the cylindrical spring just behind the threaded portion. I've driven a number of BMC cars produced before the MGB and they all had locking chokes.
Paul Hunt 2

I have an aftermarket replacement cable on my '67 that does not rotate and lock. Instead, it pulls out and is held in place by friction. It has the "C" on it. I miss the locking feature of the original unit. Ray
RAY

Ray

Thanks for your comment. I mustalso have an aftermarket cable, not NOS, as mine does not turn. BTW does your choke cable have a return spring attached to the heat shield?
I did get a copy of the original BMC parts list and it does in fact call for 4 springs as both Paul and Roger had previously mentioned


Les
Les Jacobs

Les; Yes it did originaly have a return spring on the heat shield. All that is academic now as I am currently running a Moss supercharger. Ray
RAY

This thread was discussed between 03/12/2006 and 19/12/2006

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